Plagued by vibrations

Discussion in 'Introduce Yourself' started by msrfan, Sep 17, 2010.

  1. msrfan

    msrfan Active Member

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    I've built 5 bikes with Chinese motors and had no problems until my last 3 kits. Installed in a 70's cruiser frame and vibrated very badly at speeds above 15 mph or so. Next motor did the same so I made a head brace to triangulate the mounting. It helped but is still not right. Bought a more expensive kit and it's better even without the extra brace, but not nearly good enough to give to my friend I built it for. I'm going to try a head brace on it also but it has smaller head bolts and will have to make a new one. My question is does it make a difference what frame you put these motors in? Would more substantial frame clamps help? The thin sheet metal clamps that come with the kit seem to stretch and distort easily and may not hold tight enough. I have a Panama Jack bike for my next project and will know in a couple of days if it shakes too much.
     
  2. BarelyAWake

    BarelyAWake New Member

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    Not to say that it's not engines themselves, it could well be - but I've noticed that a huge amount of the vibration usually associated with the motor is in fact coming from the "rag joint" style kit sprocket adapter (never perfectly aligned) & the dreaded chain tensioner (particularly if the chain is too tight) as the chain rattles over the hard plastic roller.

    An example of this would be bike w/a shiftkit (or one w/a sprocket adapter & no tensioner) where the vibration becomes virtually nonexistent in comparison. While it's true a single cylinder engine will always be prone to vibration - I've found it's not usually the culprit for an "unacceptable" amount unless the mounts are so loose that fastener failure is a danger (such as attempts to "pad" the mounts w/soft material like "rubber").

    Jus' figured I'd throw that out there as a possible cause ;)
     
  3. msrfan

    msrfan Active Member

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    Thanks for the insite and suggestions. I get the vibration just revving the motor with the clutch disengaged, moving or sitting still.
     
  4. kipharley

    kipharley New Member

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    welcome,If you feel comfortable with doing it I would try port matching your intake manifold and exhaust.It's reasonably easy if you have a dremill tool.
    That will make your motor run smoother and idle better.
    If you need advice just holler!If I can help I will give you mine.Use it if it makes sense to you.Kip.
     
  5. bairdco

    bairdco a guy who makes cool bikes

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    anything loose on the bike will increase vibration. i've tuned up a few bikes and found that the exhaust will cause alot of it. strap it down to the frame should help.

    i think it's kinda weird that you say "...I've built 5 bikes with Chinese motors and had no problems until my last 3 kits..."

    are you saying that 3 outta 5 have problems? those ain't good odds.
     
  6. msrfan

    msrfan Active Member

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    Thanks Kip. Good idea. I've gasket matched before with good results. I have the dremels and a large die grinders and a good assortment of burrs and bits. I think I'll get the main vibrations squared away first. I'm really leening toward the frame as the problem because the engine area is quite large with 1 1/8" tubing. All the other frames I've used were fat tube with small engine areas. I'm thinking my frame is rattling too much. I'm almost ready to try the motor in my Panama Jack. I'll post the results. When I get ready to do some porting, I may need your help.
    Hi Bairdco. The things that are loose are from the vibration. Actually I like your suggestion of clamping the exhaust. Seems to be a lot of weight hanging way out. I've really built seven, (I lost count), other bikes all using BGF motors with no extra bracing and had no problem. They all ran fairly smooth. I don't have any long range reports because some were sold to strangers that saw me riding them and offered me a good price. The others went to friends, (no profit there), and they don't ride them much. Then I bought three more from BGF and the first one vibrated a lot, so I put the second one in the same bike with the same results. That's when I made a head stay to triangulate the mounting. It was better but not good enough. So, I paid a premium for a Grubee starfire and installed it without the head brace and it was better but still not good enough. I didn't use the brace because the Grubee has 6mm head studs and the BGF's are 8mm. I plan to make a head stay for the Grubee and try it out next weekend. Also I will make a clamp for the exhaust and maybe weld in a gusset under the motor to stiffen up the enging mount area. I will tighten everything that's loose before I continue. This bike is an older cruiser, maybe a Huffy or Murray. I'm determined to use this frame.
    Another thing that has intrigued me is balancing the crank assembly. After studdying all the info and visiting my buddy at an automotive maching shop, I 've come up with a formula for balancing without disassembling the crank. Totally untested but the calculations work.
    Thanks again for the help.
     
    #6 msrfan, Sep 19, 2010
    Last edited: Sep 19, 2010
  7. msrfan

    msrfan Active Member

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    Just passing on some things that helped me considerably in building motorized bikes for the last 20 years. These chinese motors are the first 2 stroke bicycle motors I've dealt with. I have always used B & S upright motors on homemade bikes. Lawnmower shops can order 100 inch cables from Rotary Corp. These are required on some stretch frames or rear drum brakes and ape hanger bars. You just cut it to length and use a set screw barrell fitting on the cut end (sometimes referred to as a cable stop). Moped front drum brakes are a nice addition to a motor bicycle and lace up easily. You have to watch out as many are 28 spokes. I often use a moped telescoping front fork to soften the ride. A little experimenting with different bearings and cups will allow it to fit a bicycle frame. There's plenty of room for a 26" wheel if you put a small limiting slug inside the top tree. It nets about 1' to 1 1/2" travel and some models look really cool. Mounting a fender can be a bit challenging. I'll post more suggestions as I think of them. It's the least I can do for all the help I'm getting from this forum.
     

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